SAN FRANCISCO - As global populations swell, farmers are cultivating more and more land in a desperate bid to keep pace with the ever-intensifying needs of humans.

As a result, agricultural activity now dominates more than a third of the Earth's landscape and has emerged as one of the central forces of global environmental change, say scientists at the Center for Sustainability and the Global Environment (SAGE) at the University of Wisconsin-Madison.

Navin Ramankutty, an assistant scientist at SAGE, says, "the real question is: how can we continue to produce food from the land while preventing negative environmental consequences such as deforestation, water pollution and soil erosion?"

To better understand that crucial trade-off, Ramankutty and other SAGE researchers are tracking the changing patterns of agricultural land use around the world, including a look at related factors such as global crop yields and fertilizer use. Distilling that information into computer-generated maps, the scientists will present their early findings during the fall meeting (Dec. 5-9, 2005) of the American Geophysical Union.

"In the act of making these maps we are asking: where is the human footprint on the Earth?" says Amato Evan, a SAGE researcher who merged available census and satellite data to create visuals reflecting the reach of pasture and croplands worldwide. Chad Monfreda, a graduate student at SAGE, is similarly mapping the location, range and yields of over 150 individual crops reared around the planet.

The exercise is already beginning to cast light on some emerging trends. Countries such as Argentina and Brazil, for instance, have increasingly cleared forests to grow soybean, a legume that has never been a traditional crop of Latin America. Scientists say the surge in soybean production there has a lot to do with the booming demand for soy all the way at the other end of the world - in China. Meanwhile, Monfreda notes, long-time soybean farmers in the U.S. - the world's top soybean producer - are growing increasingly insecure about their place in the global market.

But scientists risk missing important regional and local trends by taking only a global approach to land use change. "There is still a large 'disconnect' between global, top-down views of changing planetary conditions, and the local, bottom-up perspective of how humans affect and live in a changing environment," says Jonathan Foley, director of SAGE.

To help bridge that gap, SAGE researchers are working towards a new "Earth Collaboratory," an unprecedented Internet-based data bank that would simultaneously draw on the knowledge of global scientists, local environmentalists and everyday citizens. Adds Foley: "[The Collaboratory] will truly be a brave new experiment that effectively bridges science, decision-making and real-world environmental practice - collectively envisioning a new way to live sustainably."

For more on SAGE's work on global land use and land cover, visit www.sage.wisc.edu/iamdata.